One of the challenges associated with any borehole system is to know the relative position and/or location of a tubular string in relation to the formation or any other reference point downhole. For example, in the oil and gas industry it is sometimes desirable to place systems at a specific position in a wellbore during various drilling and production operations such as drilling, perforating, fracturing, drill stem or well testing, reservoir evaluation testing, and pressure and temperature monitoring.
In order to determine the depth or location of a tool located on a tubular string in a wellbore, the number of tubulars, such as pipe, tubing, collars, jars, etc., is counted as the tubulars are lowered into the wellbore. The depth or location of the drillstring or a downhole tool along the drillstring will then be based on the number of components lowered into the wellbore and the length of those components, such as the length of the individual drill pipes, collars, jars, tool components, etc. However, as a tubular string increases length, e.g. at a string length of ca. 10,000 ft. or longer, the tubular string may, due to its own weight, lack stiffness and rigidity, and may become somewhat elastic and flexible. Thus, when conveying the tubular string into the wellbore, improper or inaccurate measurements of the length, depth, and location of the tubular string may take place due to inconsistent lengths of individual components such as drill pipes, tubing, or other downhole components, stretching of pipe and tubing components, wellbore deviations, or other inaccuracies, resulting in improper placement of the tubular string and associated downhole tools used for various operations.
Therefore, there is a desire for techniques assisting with accurate the placement, and determination of the locations of, downhole tools and strings in a wellbore.